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Maths Adventures

Space explorer maths quest: perimeter

A story-led junior maths adventure using rockets, planets and alien signals to measure fences, walls and safe zones around places.

Quick answer

Perimeter is the total distance around the edge of a shape. You measure perimeter by adding up all the sides of a shape, like walking around the outside of a fence or a planet's surface.

Learning outcome

By the end of this page, you will be able to measure the perimeter of any shape by adding up all the sides, whether it's a simple rectangle or a more complex polygon, and you will understand how to use perimeter in real-life space missions. Success signs:
  • You can find the perimeter of a rectangle by adding up all four sides
  • You can measure the perimeter of a shape using a ruler or counting steps
  • You can explain why knowing perimeter matters for space missions
  • You can work out the perimeter of a shape with missing side lengths

Why this matters

Perimeter is super important for space explorers! When astronauts are building habitats on other planets, they need to know how much fencing or walls they'll need to surround their safe zones. When designing rocket launch pads, engineers calculate the perimeter to make sure they have enough space for everything. Even when aliens are sending signals from their space stations, they use perimeter to know how much area they're covering. Understanding perimeter helps you plan, measure, and build in space or anywhere else!

How it works

To find the perimeter of any shape:
  1. Look at all the sides of the shape
  2. Measure each side (or count the units if it's on a grid)
  3. Add up all the side lengths
  4. Write your answer with the correct units (like metres or kilometres)
For a rectangle, you can also use a shortcut:
  • Perimeter = 2 × (length + width)
  • This means you add the length and width together, then multiply by 2

Examples you can see

Let's imagine you're an astronaut on a space mission. You need to build a safe zone around your spaceship. Your safe zone is a rectangle that is 6 metres long and 4 metres wide.
  1. First, you measure the sides:
    • Two sides are 6 metres long
    • Two sides are 4 metres long
  2. Then you add them up:
    • 6 + 6 + 4 + 4 = 20 metres
  3. So the perimeter is 20 metres
Here's a table showing how to find the perimeter of different shapes:
Shape Sides Perimeter Calculation Example
Rectangle 4 sides 2 × (length + width) Rectangle 8m × 5m = 2 × (8 + 5) = 26m
Square 4 sides 4 × side length Square 6m side = 4 × 6 = 24m
Triangle 3 sides Add all three sides Triangle 5m, 6m, 7m = 18m
Pentagon 5 sides Add all five sides Pentagon 4m each = 20m

Try it as a mini adventure

Space Explorer Mission: Planet Fence Builder You are an astronaut on a mission to Planet Zog. The alien inhabitants want you to help build a fence around their safe zone. You have a map showing the shape of the safe zone, but it's drawn on a grid where each square is 1 metre.
  1. First, you must walk around the edge of the safe zone to measure it
  2. Count how many metres you walk around the outside
  3. Write down your total perimeter measurement
Here's your safe zone shape: This shape is a rectangle that is 100m long and 100m wide.
  1. Step 1: Measure each side
    • Two sides are 100m long
    • Two sides are 100m wide
  2. Step 2: Add them together
    • 100 + 100 + 100 + 100 = 400m
  3. Step 3: The perimeter is 400 metres
Now you know how much fencing you need to build around the safe zone!

Common mistakes

  • Mistake: Forgetting to include all sides when adding up the perimeter
    Why it happens: When shapes have many sides, it's easy to miss one or two
    Fix: Use a finger or pencil to trace around the outside of the shape and count each side as you go
  • Mistake: Confusing perimeter with area
    Why it happens: Both involve shapes, so it's easy to mix them up
    Fix: Remember: perimeter is the distance around the edge, area is the space inside
  • Mistake: Not writing the correct units
    Why it happens: Children often forget to add "metres" or "centimetres" to their answers
    Fix: Always double-check that your answer has the right unit at the end
  • Mistake: Using the wrong formula for shapes
    Why it happens: Some children try to use the same method for all shapes
    Fix: Remember that rectangles have a special shortcut, but other shapes need to be added up individually

Parent and carer guide

As a parent or carer, you can help your child learn perimeter by:
  • Looking around your home for shapes with measurable sides (like picture frames, boxes, or tables)
  • Using a ruler or tape measure to find the perimeter of these objects
  • Playing a "shape hunt" game where you find different shapes and calculate their perimeters
  • Using grid paper to draw shapes and count squares to find perimeter
  • Connecting it to real-world examples like measuring a garden fence or a swimming pool
You can also ask questions like:
  • How would you measure the edge of your bedroom?
  • Can you find a shape in your house and tell me its perimeter?
  • Which shape do you think would have the longest perimeter?
Remember to be patient if your child makes mistakes. Perimeter is a new concept, and it's normal to get confused at first. The key is practice and seeing how it connects to real life.

Practice questions

  1. What is the perimeter of a rectangle that is 8m long and 5m wide?
    Answer: 26m (8 + 8 + 5 + 5 = 26)
  2. What is the perimeter of a square with sides of 6m?
    Answer: 24m (6 × 4 = 24)
  3. A triangle has sides of 7m, 9m, and 12m. What is its perimeter?
    Answer: 28m (7 + 9 + 12 = 28)
  4. What is the perimeter of a rectangle that is 12m long and 3m wide?
    Answer: 30m (12 + 12 + 3 + 3 = 30)
  5. What is the perimeter of a square with sides of 10m?
    Answer: 40m (10 × 4 = 40)

FAQ

What is perimeter?

Perimeter is the total distance around the edge of a shape. It's like walking all the way around the outside of a fence or a swimming pool.

How do I find the perimeter of a rectangle?

You can add up all four sides, or use the shortcut: 2 × (length + width). For example, a rectangle that is 5m long and 3m wide has a perimeter of 2 × (5 + 3) = 16m.

Can I find the perimeter of any shape?

Yes! You can find the perimeter of any shape by adding up all the sides. Even shapes with 5, 6, or more sides work the same way.

Why do astronauts need to know perimeter?

Astronauts use perimeter to plan safe zones, build fences, design habitats, and make sure they have enough materials for their space missions. It helps them work out how much space they need and how much fencing or wall they'll require.

What's the difference between perimeter and area?

Perimeter is the distance around the outside of a shape, while area is the amount of space inside the shape. Think of perimeter like a fence around a garden, and area like how much grass grows inside the garden.